Interleukin-6: Its role and mechanisms in rescuing depression-like behaviors in rat models of depression

Neuronal injury within specific brain regions is considered a critical risk factor in the pathophysiology of depression. However, the underlying mechanisms of this process, and thus the potential for development of novel therapeutic strategies in the treatment of depression, remain largely unknown. Here, we report that Il-6 protects against neuronal anomalies related with depression, in part, by suppressing oxidative stress and consequent autophagic and apoptotic hyperactivity. Specifically, we show that IL-6 is downregulated within the CA1 hippocampus in two animal models of depression and upregulated by antidepressants. Increasing levels of IL-6 in the CA1 region result in pleiotropic protective actions including reductions in oxidative stress and modulation of autophagy, anti-immuno-inflammatory activation and anti-apoptotic effects in CA1 neurons, all of which are associated with the rescue of depression-like behaviors. In contrast, IL-6 downregulation exacerbates neuronal anomalies within the CA1 region and facilitates the genesis of depression phenotypes in rats. Interestingly, in addition to attenuating oxidative damage, the antioxidant, N-acetylcysteine (NAC), is also associated with significantly decreased neuronal deficits and the display of depressive behaviors in rats. These results suggest that IL-6 may exert neuroprotection within CA1 neurons via pleiotropic mechanisms and may serve as a potential therapeutic target for the treatment of depression.